When you're signed in, something breaks the browser's back/forward buttons on the search results page in Firefox. To reproduce this issue, try this:
1. Go to the Bing homepage on Firefox, and make sure you're signed in.
2. Search for something.
3. Wait for a few seconds for everything to load. It takes a second or so for the problem to happen after the results show up on my computer.
4. Press back on the browser. Expected: you got back to the homepage. Actual: you stay on the search results page.
5. Click one of the search results.
6. Press back on the browser, which brings you back to the search results page.
7. Wait a second or so.
8. Press forward on the browser. Expected: you go to the page you had previously clicked on. Actual: you stay on the search results page.
Thanks for asking about what needs improvement. I've been waiting for an opportunity to talk about this on a public forum. I feel like the private feedback that I have been sending has been going into a garbage can :>